The present invention relates to a logical equals comparator circuit for comparing binary quantities to determine whether or not they are equal.
An equals comparator is usually constructed by utilizing an exclusive OR circuit applied to the operands at each bit position, and then applying the output of the latter circuit to a NOR circuit to provide an active high output. It is often necessary to ignore a certain number of least significant bits in effecting such comparisons. For example, the significance of two binary quantities may be such that they are equal if a given number of the most significant bits are equal because the remaining bits are in the noise level or otherwise unmeasurable. In such circumstances a normal comparator may indicate inequality for two equal quantities. Thus, it would be necessary to tailor the comparator to the number of significant figures of each of the quantities. Should, however, the accuracy of the quantities for some reason change then either bits having no significance would be compared or not all of the significant bits would be compared. In implementing such a comparator into MOS semiconductor technology one would not be able to change the comparator physically.
Accordingly, it is an object of the present invention to provide a method of changing the number of bits that a comparator compares without having to redesign the comparator. It is a further object of the present invention to provide a comparator that allows any number of least significant bits to be ignored.